1. Field of the Invention
The present invention relates to an optical pickup apparatus that optically records a signal to an optical record medium and/or reproduces a signal therefrom. The present invention also relates to an objective lens apparatus mounted in the optical pickup apparatus. The present invention also relates to an optical disc driving apparatus that mounts the optical pickup apparatus.
2. Description of the Related Art
As objective lenses mounted in optical pickups of related art that deal with three formats, for example, BD (Blu-ray Disc, trademark), DVD (Digital Versatile Disc), CD (Compact Disc), and so forth, the following objective lens are known (for example, Japanese Patent Application Laid-Open Nos. 2005-302163 and 2005-293770 referred to as Patent Document 1 and Patent Document 2, respectively).
In the optical pickup disclosed in Patent Document 1, a first objective lens (24) that focuses laser light having wavelengths of 400 to 410 nm to a BD (100c) and a second objective lens (25) that focuses laser light having wavelengths of 650 to 780 nm to a CD (100b) or a DVD (100a) are held by a movable block (12). In Patent Document 1, to decrease the thickness of the pickup, for example as shown in FIG. 7, in consideration of the working distance of each disc (100), namely the distance from the front surface of each disc to each objective lens, the neutral position in the focus direction of the movable block (12) is set. In other words, a two-wavelength compatible objective lens is used for a CD and a DVD because their focal lengths are nearly the same. The compatible objective lens is used, so it is a matter of course that their focal lengths are the same. Although their focal lengths are the same, since the thickness of the cover layer of the CD that laser light enters is different from that of the cover layer of the DVD that laser light enters, it is necessary to consider the working distances. As a result, the neutral position (that is a position apart from each disc by the working distance) of the focus stroke of the CD is different from that of the DVD. Thus, a total stroke takes place.
In this case, “stroke” is a range in which an objective lens is moved by an actuator. In Patent Document 1, to deal with the three formats including the BD, the objective lenses are designed so that the neutral position of the objective lens for the BD is in the middle between the neutral position of the objective lens for the CD and the neutral position of the objective lens for the DVD. As a result, the thickness in the focus direction of the optical pickup is decreased.
On the other hand, in Patent Document 2, a three-wavelength compatible objective lens that deals with the foregoing three formats is used.